Volume Fraction Dependence of Plastic and Diffusional Accommodation in High-Temperature Deformation of Ti/TiB <I>In Situ</I> Composite: Appearance and Vanishing of Load Transfer Effect

Abstract

The appearance and vanishing of the load transfer effect in the steady-state condition of composites' creep were analyzed via consideration of two accommodation processes, diffusion and plastic, which are inevitable for composites to continue creep deformation. Creep experiments were performed using model materials, Ti-5, 15 and 20 vol%TiB in situ composites, which have moderate diffusional-accommodationcontrolled creeps, good interfacial bonding and no fine dispersions. With higher strain rates than the diffusional-accommodation-controlled creep, the stress exponent of all composites was 4.5, similar to that of α-Ti, 4.3, and the strain rates decreased with increasing volume fraction of the reinforcements. Variations of the strain rate agreed with the prediction by the self-consistent potential method, and thus the load transfer effect was confirmed in this region. With strain rates near the diffusional-accommodation-controlled creep, the stress exponents of Ti-15 and 20 vol%TiB decreased to 2. With a strain rate lower than the diffusional-accommodation-controlled creep, the strain rates of the composites did not decrease with increasing volume fraction, and vanishing of the load transfer effect was observed.

Rationalization of Plastically-Accommodated Steady-State Creep of a Composite

“…Experimental observations of plastically-accommodated creep have been presented in separate papers using special model materials, in situ TiB whisker-reinforced -Ti matrix composites [31][32][33] and spherical Al 2 O 3 particle-reinforced AlMg matrix composite through ingot metallurgy. 34) …”